An electronic device having a square-law transfer characteristic, i.e., a so-called squarer, is an assumed ideal device for theoretical study of non-linear circuits. Such ideal device, for example, has been mentioned in "Non-linear Circuit Handbook" (written by the Engineering Staff of Analog Devices Inc., published by Analog Devices inc. 1974).
The transfer characteristic of such an ideal device can be described with the following mathematical equation (1): EQU Uo=KUi.sup.2 ( 1)
where
______________________________________ Uo--output voltage Ui--input voltage K--Constant ______________________________________
Up to now, such ideal device, which has been long sought, has not been satisfactorily realized in practice. The performance of existing square-law devices leaves much to be desired. The patent invention entitled "Wide Band Multiplier" (Chinese Patent No. CN 1003195B, filed on Jul. 25, 1986, announced on Feb. 1, 1989, granted on May 31, 1989), invented and filed by the same inventor of the present application, has advanced a great step towards the realization of such ideal device.
The prior art wideband multiplier is based on the conception that the backward breakdown characteristic of the backward diode is used as a conduction direction which exhibits a zero-feed through conduction characteristic, while the forward conduction characteristic of the same diode is used as the cut-off direction. One backward diode is connected with another backward diode in such a manner than when one backward diode conducts in its forward direction, the other backward diode conducts in its backward direction, and vice-versa. The multiplier constituted according to this conception provides a transfer characteristic such that the output current of the multiplier is substantially proportional to the square of the input voltage within a certain dynamic range, i.e., it has a characteristic, i=ku.sup.2, where u is the input signal voltage, i is the output signal current and k is a constant. However, the multiplier still has the following defects: when the input voltage level is high, the transfer characteristic curve departs substantially from the square-law characteristic. Therefore, the dynamic range of this device is limited, and the difference between the transfer characteristics of an A. C. signal and a D.C. signal is large. Moreover, the output circuit to be connected with the output of the multiplier must be driven by the output current of the multiplier.